Preheat the oven to 425 degrees Fahrenheit. Place the potatoes in a medium-sized saucepan, cover with cold water and a three-finger pinch of salt, and bring to a boil. Cook for 5-10 minutes until the potatoes are soft but not cooked through. Drain the potatoes, and place them on a sheet tray. Drizzle with 2 tablespoons olive oil, and season with 1 teaspoon salt. Roast in oven for 15-20 minutes until cooked through.
If the asparagus stalks are thick, cut off the bottoms and peel the outer layer with a vegetable peeler. Place on a sheet tray and drizzle with 1 tablespoon of oil. Season with 1 teaspoon salt. Roast at 425 degrees (with the potatoes) for 8 minutes for thin asparagus and 12-14 minutes for thick asparagus.
Wipe the mushrooms with a damp cloth, and cut off the bottom of the stem. Sear the mushrooms in a heavy-bottomed skillet tossed with the remaining olive oil and seasoned with the remaining salt and the pepper. Don't stir; let mushrooms sear for about 5 minutes per side until they are softened.
Clean radishes and then slice tops off, leaving a little stem on top. Peel and slice the watermelon radish if using, and place the cornichons in a small bowl. Slice the baguette into 1/4-inch thick slices. Arrange the roasted potatoes and asparagus, the seared mushrooms, baguette, radishes, cornichons, and optional watermelon radishes on a platter.
In a large bowl, toss the grated cheeses with the cornstarch, mustard powder, and ground nutmeg.
Warm up fondue pot and simmer the wine and garlic. Add cheese in handfuls, letting it melt before adding more cheese; add more wine if needed for consistency. Keep the cheese warm in the fondue pot over low heat as you dip different ingredients in the warm cheese.